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Aspirin and its pleiotropic application

Jolanta Hybiak, Izabela Broniarek, Gerard Kiryczyński, Laura,D. Los, Jakub Rosik, Filip Machaj, Hubert Sławiński, Kornelia Jankowska, Elżbieta Urasińska

PII: S0014-2999(19)30714-9
DOI: https://doi.org/10.1016/j.ejphar.2019.172762 Reference: EJP 172762

To appear in: European Journal of Pharmacology

Received Date: 11 August 2019
Revised Date: 21 October 2019
Accepted Date: 25 October 2019

Please cite this article as: Hybiak, J., Broniarek, I., Kiryczyński, G., Los, L.,D., Rosik, J., Machaj, F., Sławiński, H., Jankowska, K., Urasińska, Elż., Aspirin and its pleiotropic application, European Journal of Pharmacology (2019), doi: https://doi.org/10.1016/j.ejphar.2019.172762.

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Aspirin (acetylsalicylic acid), the oldest synthetic drug, was originally used as an anti- inflammatory medication. Being an irreversible inhibitor of COX (prostaglandin- endoperoxide synthase) enzymes that produce precursors for prostaglandins and thromboxanes, it has gradually found several other applications. Sometimes these applications are unrelated to its original purpose for example its use as an anticoagulant. Applications such as these have opened opportunities for new treatments. In this case, it has been tested in patients with cardiovascular disease to reduce the risk of myocardial infarct. Its function as an anticoagulant has also been explored in the prophylaxis and treatment of pre-eclampsia, where due to its anti-inflammatory properties, aspirin intake may be used to reduce the risk of colorectal cancer. It is important to always consider both the risks and benefits of aspirin’s application. This is especially important for proposed use in the prevention and treatment of neurologic ailments like Alzheimer’s disease, or in the prophylaxis of myocardial infarct. In such cases, the decision if aspirin should be applied, and at what dose may be guided by specific molecular markers. In this revived paper, the pleiotropic application of aspirin is summarized.

KEYWORDS: aspirin; anticoagulant; cardiovascular; cancer; cyclooxygenase; pre-eclampsia

1. Aspirin – a historic perspective

Aspirin has been manufactured since the end of XIX century, however its precursors have been present in human medicine for thousands of years. Ancient Egyptians and Sumerians used willow bark and leaves against inflammatory conditions caused by injury and to relieve joint pain. Moreover, the Khoikhoi people of South Africa and the Indigenous peoples of North America, having discovered these properties completely independently, used the willow extracts to cure fever, osteoarthritis and headache (Al-Khalifa, 1993; Lichterman, 2004; Shara and Stohs, 2015; Volmink, 2008; Wood, 1993).

The active agent that is responsible for analgesic, antipyretic and anti-inflammatory properties of willow is salicin. Salicin is metabolized by intestinal flora into saligenin, and then further metabolized by the liver into salicylic acid – a substance that differs from aspirin through a lack of an acetyl group (Shara and Stohs, 2015).

For years the methods of salicylic acid and salicylates synthesis were improving alongside discoveries concerning their medical use (Lagan, 1876; Montinari et al., 2019; Roche, 2006). Finally, on August 10, 1897, aspirin was created – a derivative of salicylates that did not share the adverse effects of sodium salicylate, like nausea, gastric irritation or tinnitus (Lichterman, 2004; Montinari et al., 2019). On that day, Bayer’s laboratories obtained acetylsalicylic acid in its purest form using a relatively reliable, efficient and simple
process. Aspirin was then patented in the United States on February 27, 1900. Initially it was sold as a powder, however in 1904 aspirin became the first industrially produced drug available in tablet form worldwide – a fact indicative of its wide commercial success (Lichterman, 2004; Shara and Stohs, 2015).

In 1971, JR Vane further proposed that aspirin and other non-steroidal anti- inflammatory drugs acted through dose-dependent inhibition of prostaglandin biosynthesis. This discovery was groundbreaking, as it explained the pleiotropic effects of not only aspirin,but also other non-steroid anti-inflammatory drugs (NSAIDs) through a single mechanism of action (Vane, 1971).

2. Aspirin antiplatelet effect

COX (prostaglandin-endoperoxide synthase/cyclooxygenase) is a monotopic integral enzyme, which means it is permanently attached to a cell membrane from one side (Fowler and Coveney, 2006). It exists in 2 main isoforms (COX-1 and COX-2), both possessing a fatty acid oxygenase activity and a peroxidase activity. A third COX enzyme is a splicing variant of COX-1 gene, but its involvement in response to aspirin is unclear (Andrew O. Maree, 2004). COX-1 is the constitutive form of the enzyme – present in all tissues, while COX-2 is expressed in inflammatory states in response to reactive oxygen species, cytokines, endotoxins or growth factors (McAdam et al., 1999). They accept arachidonic acid (AA) as a substrate and form prostaglandin H2 (PGH2) as a product, which in turn may be converted to thromboxane A2 (TXA2), prostacyclin or other prostaglandins e.g. prostaglandin E2 (PGE2) through appropriate enzymes. Thromboxane is responsible for platelet aggregation, where it acts as a vasoconstrictor and as a smooth cell mitogen (Moncada and Vane, 1979) (see figure 2).

The anti-platelet effect of aspirin results from disrupting the function of COX-1 and COX-2. It causes irreversible acetylation of a serine in position 530 in COX-1 and in position 516 in COX-2, limiting the access of arachidonic acid to the catalytic active site of the enzyme, and thus preventing further synthesis of thromboxane (Lecomte et al., 1994; Roth et al., 1975). Aspirin has a much greater affinity for COX-1 than for COX-2 as it is about 170 times more effective in inhibiting it (Vane et al., 1998). However, along with blocking thromboxane production, aspirin also blocks synthesis of prostaglandins, most importantly – prostacyclin. Under physiological conditions, thromboxane and prostacyclin are in homeostatic balance, having opposite effects on platelet aggregation and vascular activity. One could assume that suppressing prostacyclin production would disqualify aspirin from having an anti-platelet effect, but that is not the case. This paradox results from the fact that thromboxane is synthesized within platelets, but prostacyclin is synthesized within endothelial cells. Unlike most cells, platelets are anucleate and are therefore incapable of synthesising new proteins to replenish their COX-1 population. As a result, when aspirin reaches bone marrow megakaryocytes and platelet precursors, their thromboxane production becomes blocked for the entire lifespan of the cell. On the other hand, endothelial cells are translationally active, and are thus able to restore their COX activity, and consequently, prostacyclin production. This mechanism also explains why anti-platelet effects of aspirin require lower doses than aspirin’s anti-inflammatory, analgesic and antipyretic properties (Patrono et al., 2017). Clinical trials have shown that daily doses of 30-160mg of aspirin were sufficient to impair thromboxane production, while much higher doses offered no additional benefit, which was consistent with saturability of platelet COX-1 inactivation (Patrono, 1994).

There are also reports of additional mechanisms of action, besides aspirin’s antiplatelet properties. It has been found to reduce the generation of thrombin, and consequently weaken thrombin-mediated coagulant reactions. Aspirin also acetylates lysine residues in fibrinogen, which results in increased fibrin clot permeability and enhanced clot lysis. With high doses of aspirin, this mechanism directly promotes fibrinolysis. The effectiveness of these additional antithrombotic effects strongly varies between patients, which may be due to common genetic polymorphisms such as the Leu33Pro β3-integrin or Val34Leu factor XIII mutations. These effects might also explain cases of aspirin resistance found among patients however, the clinical relevance of these observations is unclear (Undas et al., 2007). Aspirin also inhibits the neutrophilic activation of platelets by utilizing nitric oxide and cGMP (López-Farré et al., 1995).

Aspirin is the only irreversible inhibitor among NSAIDs – a property it owes to the acetyl group in its chemical structure. In fact, other NSAIDs (e.g. ibuprofen or naproxen) may compete with aspirin over access to the COX-1 docking site – Arg120. This prevents subsequent acetylation and undermines the antithrombotic effect of aspirin (Li et al., 2014).

On the other hand, Dual Antiplatelet Therapy, where aspirin combines with one other antiplatelet drug is the most common form of antiplatelet therapy. Drugs used in concert with aspirin include: clopidogrel, prasugrel, ticagrelor, vorapaxar, dipyridamole and rivaroxaban. It is important to note that these drugs do not compete with aspirin because they affect different signalling pathways (Patrono et al., 2017).
The antiplatelet effect of aspirin is most often used in secondary prevention, as opposed to primary prevention. This means that it is prescribed to patients with increased cardiovascular risk, usually >20% over 10 years. This is because aspirin increases chances of bleeding, such as intracranial hemorrhage or gastrointestinal bleeding. In primary prevention for patients with lower cardiovascular risk, the dangers of aspirin use may outweigh its benefits. As a result, different medical organizations have varying recommendations concerning primary prevention of cardiovascular disease (CVD) through aspirin. In general, aspirin is recommended for patients with at least moderate CVD risk, and without increased risk of bleeding (Patrono et al., 2017; Vries et al., 2015). Aspirin found a use in preventing complications after surgical interventions (e.g. implantation of prosthetic heart valves, revascularization procedures) and in prophylaxis of the following conditions: angina pectoris, myocardial infarction, ischemic stroke, and thromboembolic stroke – including those accompanying atrial fibrillation. It is also used to treat antiphospholipid syndrome, angina, ischemic bone necrosis, myocardial infarction, transient ischemic attack and ischemic stroke .

The anti-platelet properties of aspirin have also been used in certain dermatological conditions, depending on whether their aetiology involves platelet aggregation. Type I erythromelalgia is a clinical condition associated with thrombocythemia, and occlusion of the vasculature of digital arteries and arterioles. It manifests as a burning sensation and redness over the extremities (Michiels et al., 1985). The dose of aspirin used ranges from 325 to 650 mg per day, with a 500 mg dose of aspirin lasting for 3 days. This long-lasting effect of aspirin can also be used in diagnostics for myeloproliferative disease-linked secondary erythromelalgia (Kurzrock and Cohen, 1991; Preston, 1983). Aspirin has also been suggested as a treatment in necrobiosis lipoidica diabeticorum – a rare skin condition associated with diabetes mellitus and characterized by degenerative and granulomatous changes (Reid et al., 2013). Although its aetiology is unclear, it has been postulated to be caused by the deposition of immune complexes in the walls of blood vessels and enhanced aggregation of platelets (Imtiaz and Khaleeli, 2001). In two uncontrolled trials, aspirin was administered in low doses, either alone or in conjunction with dipyridamole. The treatments resulted in marked improvement of most, or all patients (Heng et al., 1989; Karkavitsas K, 1982). However, studies by Beck et al. and Statham et al. challenged the therapeutic benefit of aspirin in necrobiosis lipoidica diabeticorum (Beck HI, 1985; Statham B, 1981).

3. Aspirin in cancer prevention and treatment

Chronic inflammation increases the risk of developing CVDs, cerebrovascular disease, and cancer. Studies published in the last two decades, strengthen the hypothesis that long-term aspirin administration may protect against cancer and reduce mortality caused by cancer (Algra and Rothwell, 2012; Cook et al., 2013; Jacobs et al., 2007; Rothwell et al., 2012). The results of a large observational study comprising data from 8 randomised trials with more than 25,000 individuals is also worth mentioning (Rothwell et al., 2011). They showed that low- dose aspirin taken daily reduced the long-term mortality rate from several common cancers during and after the trials.

There is growing evidence from observational studies, that aspirin can be a promising cancer-preventive agent (Patrono, 2015; Thun et al., 2012). Therefore, many studies are focused on determining the most effective aspirin dose, several of them concern colorectal cancer. They suggest that aspirin taken at doses of less than 100 mg daily, decrease the colorectal cancer incidence and mortality rate (Chan et al., 2008; Cook et al., 2013; Rothwell et al., 2010). Evidence of a 27% reduced risk of colorectal cancer for regular aspirin use was reported by Bosetti et al. (Bosetti et al., 2012). Low-dose aspirin use has been recommended for the primary prevention of cardiovascular disease and colorectal cancer by U.S. Preventive Services Task Force (Bibbins-Domingo and Force, 2016). This recommendation is to be applied in patients aged 50 to 59 years. Other requirements that they must meet, include a 10% or greater 10-year CVD risk, decreased risk for bleeding, and the will to take low-dose aspirin daily for at least 10 years. However, Rothwell et al. suggests that the same dose does not have a protective effect on all patients and the optimal aspirin dose depends on the age and bodyweight of the patient (Rothwell et al., 2018).

Similar reports concerning other types of cancer have also been published. For example, in patients diagnosed with breast cancer, low-dose aspirin use is associated with reduced mortality rate, including breast cancer-specific mortality (Fraser et al., 2014). Regular aspirin use was associated with a 39% reduced risk of breast cancer. Association was not modified by familial risk, and remained consistent regardless of whether the patterns were BRCA1 and/or BRCA2 mutation carriers, the patients estrogen receptor status, and the patients attained age (Kehm et al., 2019). A risk of ovarian cancer is reduced by 20-34% among women taking low-dose aspirin daily (<100mg) (Trabert et al., 2014). Some data has shown that aspirin at a dose of 75 mg/day, is as effective as higher doses; (Rothwell et al., 2011; Rothwell et al., 2010; Rothwell et al., 2012). Pooled analysis of 2 prospective US cohort studies on health individuals compared nonregular use and regular aspirin use (≥2 standard-dose [325-mg] tablets per week) on hepatocellular carcinoma rate. Reduced hepatocellular carcinoma hazard ratio was associated with the aspirin treatment dose and the duration of the treatment over 5 years (Simon et al., 2018). Large prospective studies provided evidence that regular use of aspirin or non-aspirin NSAIDs may reduce the risk of non-cardia gastric cancer; however, was not associated with reduced risk of oesophageal adenocarcinoma (Abnet et al., 2009). Analysis of the Physicians' Health Study provided very promising results in terms of prostate cancer. Downer et al. (Downer et al., 2017) concluded that regular aspirin use (325 mg, every other day) was associated with a lower risk of fatality caused by prostate cancer among all participants. Post diagnostic use of aspirin was associated with improved survival after diagnosis, consistent with a potential inhibitory effect of aspirin on prostate cancer progression. Aspirin treatment may also be a strategy for reducing the risk of prostate cancer for patients at high risk of BRCA mutation (Cossack et al., 2014). There are also reports indicating an insignificant anticancer effect of aspirin administered for up to 4 years (Burn et al., 2008; Cole et al., 2009). Results of Bosetti et al. (Bosetti et al., 2012) presented a decrease in colorectal cancer risk, however they found no statistically significant association between aspirin uptake and pancreas, endometrium, ovary, bladder, or kidney cancer. Recently Haykal et al. (Haykal et al., 2019) reported meta-analysis on the basis of 16 randomized controlled trials, where mean follow-up was 5.48 years. They found that aspirin was not associated with a significant reduction of cancer-related mortality or cancer incidence compared to placebo. They even concluded that the use of aspirin for primary prevention of cancer caused higher rates of bleeding with no significant benefit in cancer primary prevention. A systematic review based on nine published epidemiologic studies was carried out to assess the aspirin and non-aspirin NSAIDs potential as chemopreventive agents of squamous cell carcinoma. The observed reduced risk was not statistically significant for the aspirin treatment, however significant reduced risk was observed for non-aspirin NSAIDs (Muranushi et al., 2015).Khalaf et al. (Khalaf et al., 2018) evaluated aspirin and non-aspirin NSAID use, and the risk of pancreatic adenocarcinoma in two prospective cohort studies. Results of the analysis showed that the use of aspirin or non-aspirin NSAIDs was not associated with reduced pancreatic cancer risk. However, in subgroup analysis among participants with diabetes, regular aspirin use was associated with reduced pancreatic cancer risk. Authors of the meta-analysis claim that results of the epidemiologic studies are heterogeneous across published papers, and dose-risk and duration-risk relationships are still unclear (Haykal et al., 2019; Muranushi et al., 2015). The role of aspirin as a primary prevention of cancer is still controversial and may be more beneficial in certain cancers over others. Moreover, evaluation of benefits versus risk, need to be assessed (Brotons et al., 2015). 3.1. Biomarkers for a potential aspirin anticancer therapy To ensure a positive balance of benefits and risks from aspirin, it seems that more personalised assessment of the advantages and disadvantages is required, and the biomarkers for the anticancer effects of aspirin need to be established (Coyle et al., 2016). It was shown that response to aspirin prevention of cancer depends on the BRAF gene status, which is an important gene in a RAS-proliferative signalling pathway. Wild-type BRAF individuals respond better to the regular aspirin use because they possess a lower risk of developing colorectal cancer when compared to mutated-type BRAF individuals. Results suggest that mutated-type BRAF cells remain resistant to aspirin’s anticancer effects (Nishihara et al., 2013). After colon cancer diagnosis improved, overall survival improvement upon aspirin supplementation was observed in wild-type BRAF-tumors however not in mutated-type BRAF-tumors. Such correlation relating to KRAS-mutation status was not observed (Frouws et al., 2017).Liao et al. (Liao et al., 2012) proposed mutation status of PIK3CA as a predictive molecular biomarker for adjuvant aspirin therapy of colorectal cancer. Regular use of aspirin after diagnosis was associated with longer survival among patients with mutated-type PIK3CA colorectal cancer, but not among patients with wild-type PIK3CA colorectal cancer. The use of aspirin and PI3K pathway inhibitors as a combination therapy for targeting breast cancer was proposed (Henry et al., 2017). The presence of mutations in both PIK3CA and KRAS was associated with greatest aspirin sensitivity in breast cancer cells (Turturro et al., 2016). Fink et al. (Fink et al., 2014) took insight into hydroxyprostaglandin dehydrogenase 15 - (nicotinamide adenine dinucleotide) (15-PGDH, HPGD), a metabolic antagonist of prostaglandin-endoperoxide synthase 2 (PTGS2, cyclooxygenase 2) - related pathways which is down-regulated in colorectal cancers (Tai et al., 2007). They assessed mRNA 15-PGDH expression level in normal mucosa from colorectal cancer resection in 270 patients documented in the Nurses' Health Study and the Health Professionals Follow-Up Study. Regular aspirin use was associated with lower incidence of colorectal cancers arising in association with high 15-PGDH expression, however not with low 15-PGDH expression in normal colon mucosa. This suggests that 15-PGDH expression level in normal colon mucosa may serve as a biomarker that may predict stronger benefit from aspirin chemoprevention. A differential antitumor effect of aspirin according to immune checkpoint programmed cell death 1 (PDCD1, PD-1) status was observed (Hamada et al., 2017). The association of aspirin use with colorectal cancer survival is stronger in patients with CD274- low tumors than with CD274-high tumors.Han et al. (Nan et al., 2015) tested gene and environment interactions between regular use of aspirin and/or NSAIDs and single-nucleotide polymorphisms (SNPs) in correlation with risk of colorectal cancer. They aimed to identify common genetic markers that may indicate differentiation in aspirin or NSAID efficiency as chemopreventive agents. The different responses to aspirin treatment were associated with genetic variation at 2 SNPs on chromosomes 12 and 15. 4. Aspirin in pre-eclampsia prevention Preeclampsia is a disorder that occurs during human pregnancy, diagnosed as early as during the second trimester. It is caused by placental dysfunction, which occurs in the first trimester. Its key diagnostic criteria are arterial hypertension and proteinuria. When proteinuria is absent, preeclampsia is diagnosed when new-onset hypertension is accompanied by a minimum of one of the following: thrombocytopenia, renal insufficiency, impaired liver function, pulmonary oedema, cerebral symptoms, or visual symptoms (Gynecologists, 2013). Invading decidua is a result of interactions between trophoblast cells, metalloproteases and the extracellular matrix. The process is controlled by growth factors, enzyme inhibitors and is affected by the expression of integrins and cadherins (Merviel et al., 2004). Endometrial maturation association with the development of branches of uterine arteries, i.e. spiral arteries, depends on endocrinal balance. Ovarian hormones and growth factors responsible for neoangiogenesis are crucial for these transformations. Another important step in this process is the conversion of spiral arteries into large-calibre capacity vessels (Wang et al., 2009). Effective circulation is possible due to haemostasis and an advantage of thrombomodulin and plasminogen activators over pro-coagulant factors. It is vital to provide enough blood perfusion to the placenta. Immunological imbalance, extensive inflammatory reaction, abnormalities of early pregnancy in the process of placentation, and cytotrophoblast cells invasion all have a potential genetic background and reveal themselves in the second trimester (Merviel et al., 2004). These anomalies lead to vasoconstriction, the formation of microthromboses, and an imbalance of serum concentrations of arachidonic acid derivatives. This pathological process may be stopped by removing the dysfunctional placenta. It is important to prevent preeclampsia development to avoid premature delivery or abortion. Aspirin might become an efficient therapeutic option due to its anticoagulant and anti- inflammatory properties. Acetylsalicylic acid may restore favourable arachidonic acid serum concentrations for the fetus and prevent decline in fetoplacental blood flow. Low doses of acetylsalicylic acid may also prevent endothelial cell dysfunction through sFlt1 inhibition via the JNK/AP-1 pathway (Lin et al., 2019). Aspirin possibly down-regulates genes responsible for encoding coagulation factors or lipid transport (Ducat et al., 2019). Aspirin may become a beneficial option for a treatment because of its high transfer through the blood-placenta barrier and its ability to present its therapeutic properties even if received in low doses of 50- 150 mg. However, doses higher than 75 mg/day were found to be more effective (Duley et al., 2001). Meta-analysis on more than 30 000 women proved the effectiveness of aspirin. Slight reduction was observed in preeclampsia and adverse perinatal outcomes (Duley et al., 2007). In 2013, the American College of Obstetricians and Gynecologists defined daily low-dose aspirin administration beginning in the first trimester in a population with very high risk, as a qualified recommendation with a moderate quality of evidence (Gynecologists, 2013). Nicotinamide nucleotide transhydrogenase in such a population is far lower than in a population at moderate risk (19 vs 119) (Duley et al., 2007). Apart from aspirin, only calcium supplementation was found effective in preeclampsia prevention in risk groups in randomized clinical trials (José Geraldo, 2017). Studies on the influence of aspirin on preeclampsia occurrence did not reveal significant adverse outcomes, for example, premature closure of ductus arteriosus Botalli or bleedings, but it is too soon to exclude the existence of any negative long-term effects on the offspring. Aspirin is a safe drug in the context of preterm prelabour rupture of membranes. 150 mg Aspirin (per orally, nocte) should lead to a reduction in prevalence of preterm prelabour rupture of membranes in a group of women at high risk for developing early-onset preeclampsia, however, it is currently too soon to verify this hypothesis (El-Achi et al., 2019). Before the therapy, an IVY bleeding time test should be performed and only results below 8 minutes qualify for the treatment (Merviel et al., 2004). During therapy, this test might be useful in adjusting the dose. The main tasks that lie ahead are to check if acetylsalicylic acid should be administered to all women or only women in high risk, and to find a safe and efficacious dose for women with underlying medical illnesses. Women, who suffered from more common illnesses like hypertension or nephropathy before pregnancy, are prone to respond ineffectively to the aspirin treatment (Heyborne, 2000; Merviel et al., 2004). Balancing risks (Schrör, 2016) and potential benefits (not only preeclampsia, but also other vascular event preventions) are potential directions that need to be explored, as well as if it is more beneficial to administer aspirin from conception or to wait longer than ten weeks (Merviel et al., 2004). Benefits from treatment in the last weeks of pregnancy are also being discussed. Stopping therapy in order to avoid perinatal bleedings is questionable. 5 Aspirin therapeutic potential for mental and neurobiological illnesses Neuropsychiatric disorders are mental disorders that manifest themselves because of a disfunction in the central nervous system. The organic backgrounds of many of these disorders are not fully understood, which makes research aiming to find novel therapies difficult. It is suspected that inflammation and oxidative stress are crucial for the development of most of these diseases. Alzheimer’s disease (AD), which may be accompanied by intracerebral vascular disease, is the most common form of dementia. It affects mostly people at the age of 65 or older, but early onset familial Alzheimer's disease is a problem affecting whole generations, very often patients younger than 65. Degeneration of synapses and neurons leads to a progressive loss of memory, dementia. Pathological presentation of the brain is characteristic for AD. During post mortem examination, brain atrophy is easily visible. Histopathologic images present neurofibrillary tangles from hyperphosphorylated tau proteins inside cell bodies and beta amyloid plaques outside of neurons. In the last decade, few hypotheses on AD development have been verified. Some have become basis for novel, however ineffective therapies. β-amyloid, whose presence is responsible for inflammatory reactions, is responsible for mitochondrial disfunction. It makes neurons more vulnerable to ischemic reactions (Schrör, 2016). This process does not lead to apoptosis, but rather causes cell degeneration. A progressive loss of synapses between neurons is affected by diseased neurons and leads to the presence of disease symptoms. Pathogenesis of AD reveals a few potential therapeutic points: β-amyloid and its precursor synthesis, cells participating in inflammation, and the production of pro-inflammatory chemokines. Clinical trial NCT01953601 failed to prove that verubecestat, a β-site amyloid precursor protein-cleaving enzyme 1 (BACE-1) inhibitor, is effective in prodromal Alzheimer prevention (Egan et al., 2019). Blockade of β-amyloid production was, according to result of clinical trial NCT01739348, inefficacious in the course of therapy of patients with mild-to- moderate AD (Egan et al., 2018). Failure of BACE-1 inhibitors (verubecestat and atabecestat) (Knopman, 2019) was not the first unsuccessful attempt to put into practice theories based on β-amyloid; antibodies targeting this substance failed to succeed a few years prior. Aspirin influence on the formation of amyloid conglomerates was verified and the results were promising in diverse studies (Harris, 2002; Hirohata et al., 2005). However, comments on trials verifying anti-amyloid strategies suggest that it is high time for a new, dissimilar solution (Knopman, 2019; Panza et al., 2018). Aspirin, due to its anti-thrombotic properties, is useful in prevention of deterioration of cognitive function caused by ischemia. It is possible that because of its targeting apolipoprotein E isoforms and anti-inflammatory properties, acetylsalicylic acid is able to prevent neuroinflammation, and hence, oxidative stress development and AD progression (Berk et al., 2013). One of the postulated probable mechanisms justifies the aforementioned association with inhibiting COX-2, which is constitutively expressed in neurons (Schrör, 2016). However, microglia cell activity, which is more important for inflammation, does not strongly depend on COX-2 (Firuzi and Praticò, 2006; Hoozemans et al., 2006). Several clinical trials aiming to verify the possibility that acetylsalicylic acid halts the progress of AD have been conducted. One of them found that this well-known NSAID may decrease hyperphosphorylation of tau proteins (Tortosa et al., 2006). According to another piece of research aspirin, as opposed to other checked NSAIDs, did not reduce the risk of AD and dementia (Szekely et al., 2008). Epidemiological studies were performed to examine the association between acetylsalicylic acid treatment and AD development. One of them followed almost 7000 people aged 55 years or older for 7 years. It found a connection between NSAID intake and reduced risk of AD. The OR varied from 0.2 (0.05-0.83) for long-term use (min. 2 years) to insignificantly reduced risk for short intake (in 't Veld et al., 2001). Metanalysis by Wang et al. presented similar results. This study proved that AD risk is reduced for both aspirin [RR = 0.77 (0.63–0.95)], and non-aspirin NSAIDs users [RR = 0.65 (0.47–0.88)] (Wang, 2015).Contrastingly, trials have also been conducted for which results were opposed to those aforementioned. Collected data suggest that aspirin might not be effective in treating either vascular dementia (Williams et al., 2000) or AD (Group, 2008), and NSAIDs do not prevent AD (Aisen et al., 2003; Group, 2015; Lyketsos et al., 2007). No sufficiently strong indications exist to recommend acetylsalicylic intake to prevent AD. Well-known side-effects of NSAIDs are not out-weighted by benefits of such treatments. Low-doses of acetylsalicylic acid, which are beneficial for people with coronary heart disease, are probably ineffective in dementia prevention. 6. Other (experimental) aspirin applications As a low cost and easily available medication, aspirin is a subject of investigation in many fields. Sepsis is a leading global cause of morbidity and mortality, and is more common at the extremes of age. Moreover, the cost of in-hospital care for elderly patients with sepsis is significant. Double-blind, randomized, placebo-controlled studies in healthy volunteers, and ex vivo stimulation experiments using monocytes of septic patients were conducted. Treatment, but not prophylaxis, with low-dose acetylsalicylic acid partially reverses endotoxin tolerance in humans, in vivo by shifting response toward a proinflammatory phenotype. This acetylsalicylic acid–induced proinflammatory shift was also observed in septic monocytes, signifying that patients suffering from sepsis-induced immunoparalysis might benefit from initiating acetylsalicylic acid treatment (Leijte et al., 2019). ASPREE sub- studies conducted in Australia, were designed to determine whether aspirin safely reduces sepsis-related deaths and hospitalisations in older people (Eisen et al., 2017). Age-related hearing loss causes disability in the elderly. Low-grade inflammation and microvessel pathology may be responsible for initiating or exacerbating some of the hearing loss associated with aging. A growing body of evidence demonstrates an association of hearing loss with cognitive decline. A shared etiological pathway may include a role of inflammation, alongside vascular determinants. The ASPREE-HEARING study aims to determine whether low-dose aspirin decreases the progression of age-related hearing loss, and if so, whether this decrease in progression is also associated with retinal microvascular changes and/or greater preservation of cognitive function (Lowthian et al., 2016). Antiviral aspirin properties were observed in vitro. High efficiency against influenza A H1N1 virus was reported. The antiviral activity against further respiratory RNA viruses was less distinct. Respiratory syncytial virus was minimally inhibited. However, the activity of aspirin against rhinoviruses was more pronounced. Aspirin demonstrated antiviral activity against all human rhinoviruses (HRV), but the effect on members of the "major group" viruses, namely HRV14 and HRV39, was greater than on those of the "minor group," HRV1A and HRV2 (Glatthaar-Saalmüller et al., 2017). HIV infections have increased risk for CVD (O’Brien et al., 2019). Aspirin antiplatelet and immunomodulatory properties were used to study HIV-1 infected patients. 1 week of low-dose aspirin attenuates platelet activation and immune activation in HIV-1-infected, and virologically suppressed adults, on antiretroviral therapy. This benefit may protect from prothrombotic state in HIV-1 patients (O'Brien et al., 2013). The effect of the use of aspirin in kidney transplant recipients was investigated (Cheungpasitporn et al., 2017). The meta-analysis demonstrates that administration of aspirin in kidney transplant recipients is associated with reduced risks of allograft failure, allograft thrombosis, and major adverse cardiac events or mortality. However, it did not reduce the risks of allograft rejection or delayed graft function-loss. Reduced risk of allograft vasculopathy was observed in long-term follow up in patients after heart transplantation (Peled et al., 2017). During 15 years of follow up, the rate of cardiac allograft vasculopathy in aspirin treated patients in comparison to non-aspirin treated patients was: 7% vs 37% respectively. Association between bone mineral density and the use of NSAIDs, including aspirin, was investigated (Carbone et al., 2003). Data suggests that the combination of relative COX-2 selective NSAIDs and aspirin, is associated with higher bone mineral density at multiple skeletal sites in men and women. In vitro studies on murine bone marrow stromal cells, showed that low dosage of aspirin promotes cell growth and osteogenic differentiation (Du et al., 2016). Information about registry and results of publicly and privately supported clinical studies of human participants conducted in 210 countries are available on the web (https://clinicaltrials.gov) (Medicine). The subjects of currently active studies on aspirin are presented in the table 1. 7. Conclusions Aspirin, a well-known drug sold since 1904, has become the most commonly used drug in the world. It is routinely applied as an analgesic, anti-inflammatory and antipyretic drug. In recent years it has become more broadly applied, although not in proiamry prevention of cardiovascular disease, but only in secondary prevention. Its anti-inflammatory properties prompted its use in prevention of inflammation-related cancers e.g. colon cancer. Aspirin, due to its low cost, and wealth of clinical experience, is the subject of study in a growing number of fields like neurological diseases, viruses related diseases, or bone (patho-)physiology. However, aspirin may cause acute bleeding or gastric mucosa injury, hence, the assessment of benefits and harms is required. Continuous research on the molecular mechanism of aspirin’s action will reveal additional predictive biomarkers, allowing for more focussed, safer, and more efficient application of this simple and effective drug. Figures Legends Fig. 1. The history of aspirin discovery in brief (Collier and Shorley, 1960; Gibson, 1949; Hamberg et al., 1975; Hemler and Lands, 1976; Jeffreys, 2004; Lichterman, 2004; Montinari et al., 2019; Piper and Vane, 1969; Sneader, 2000; Sneader, 2005; Vane, 1971; Wood, 2015). Fig. 2. Cyclooxygenases in cancerogenesis and metastasis Cyclooxygenase 1 (COX-1) is constitutively expressed in a wide variety of cells. The expression of cyclooxygenase 2 (COX-2) is inducible and its overexpression is observed in cancer cells. Both COX isoforms synthetize prostaglandin H2 (PGH2) from arachidonic acid (AA). Then, from PGH2 are generated thromboxane A2 (TXA2) and prostaglandin E2 (PGE2). During oncogenesis the level of PGE2 is significantly elevated (Kurtova et al., 2015; Zelenay et al., 2015), which leads to enhanced tumor proliferation, tumor angiogenesis, tumor immune escape and inflammation (Ghosh et al., 2010; Zelenay et al., 2015). Moreover, the generation of TXA2 affects tumorigenesis too. It promotes angiogenesis (Nie et al., 2000; Pradono et al., 2002) and metastasis by facilitation of interactions between platelets-tumor cells and tumor cells-endothelial cells (Matsui et al., 2012). Additionally, TXA2 induces circulating platelets activation. Aspirin inhibits COX irreversibly. Because platelets do not have a nucleus, it is possible to obtain nearly complete inhibition of platelet COX-1 by a daily use of aspirin in a low dose (Eikelboom et al., 2012; Patrignani et al., 1982; Sostres et al., 2014). To inhibit COX-2 in nucleated cells, a use of higher aspirin doses is required, because nucleated cells have het capacity to NSC 27223 synthesize COX de novo (Eikelboom et al., 2012).